1. Field of the Invention
The present invention relates to cadmium sulfide photovoltaic cells of improved efficiency and resistance to short circuits. More particularly, the invention relates to cadmium sulfide cells having an increased voltage output characterized by a tri-layer construction in which the shortbarrier is a layer within the cadmium sulfide semi-conductor layer.
2. Description of the Prior Art
The preparation of cadmium sulfide thin film photovoltaic cells in general is well known. However, a great deal of research effort is still expended in the development and improvement of such photovoltaic cells in order to provide greater cell efficiency and economic feasibility.
U.S. Pat. No. 2,820,841 concerns a typical polycrystalline cadmium sulfide photovoltaic cell comprising a cadmium sulfide layer, a photovoltaic barrier layer, usually copper sulfide, a conducting electrode layer, and a collecting electrode layer.
U.S. Pat. No. 3,880,633 concerns the continuous fabrication of photovoltaic cells by spray deposition of materials on a glass substrate in which a transparent tin oxide layer is applied to the glass as the conducting electrode layer, followed by spraying cadmium chloride and N,N-dimethylthiourea aqueous solution doped with aluminum chloride over the transparent tin oxide conducting electrode layer.
U.S. Pat. No. 4,086,101 concerns cadmium sulfide photovoltaic cells in which short circuits caused by copper migration through the cadmium sulfide layer are inhibited by incorporating aluminum throughout the cadmium sulfide layer.
U.S. Pat. No. 4,143,235 concerns cadmium sulfide photovoltaic cells having improved efficiency due to a cadmium sulfide bi-layer formed by depositing at a first temperature an initial layer of cadmium sulfide in contact with a substrate layer and depositing a second layer of cadmium sulfide at a second temperature which is at least about 20.degree. C. different than the first deposition temperature.
The prior art developments as discussed above have resulted in improvements in the efficiency and economics of thin film cadmium sulfide photovoltaic cells, including their resistance to short circuits. However, there is a continuing need for improvement of the efficiency of such cadmium sulfide photovoltaic cells.